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Calculation of required aluminum thickness for carrying 3.5 A


Q. I have to deposit Aluminum and I know its width is 400 micrometer and I want to calculate the thickness of the deposition so that the Aluminum can carry 3.5 Amps and I have no details about the length of the deposition.

Please help me out.

Gangadharan Sivaraman
Texas Tech University - Lubbock, Texas

First of three simultaneous responses -- 2002

A. I am 100 % positive that you can find data on the load capacity of aluminum in the TT Library.
1. Pure aluminum or alloy? it makes a big difference
2. Load capability of any metal is dependent on the temperature rise that you can live with. You did not state!
3. Just how do you plan on depositing the aluminum?

James Watts
- Navarre, Florida

Second of three simultaneous responses -- 2002

A. I assume you are designing a circuit! Your concern needs to be current density and not length. Your spec of 3.5 A is a very high current to be carried by a 0.4 mm Al strip. If you don't use enough thickness, you will experience "electromigration". Check some literature on that subject. A lot has been studied and published in the context of ICs and hybrids.

Having suggested that, there are some rules of thumb in the design. Determine the thickness based on the current density not to exceed 1 megamp per cm sq. or less. Then some (50% to 100%) safety factor for coating defects. As a good start, I would consider 10E5 density and find cross section, then determine thickness based on density of Al. Thicker the coating, better off you will be. Then worry about process economics.

Mandar Sunthankar
- Fort Collins, Colorado

affil. link
"Circuit Designer's Companion"
from Abe Books


Third of three simultaneous responses -- 2002

A. In the macro world we use 500-600 Amps per square inch of cross section as a good safe rating for aluminum. That probably has very little to do with the answer you need for your micro device, but there it is for reference :-)

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


Q. Dear James Watts, Mandar Sunthankar, and Ted Mooney,

I would like to Thank you for your valuable comments and I have used the current density to find the thickness and I am enclosing the solution with this.

I request you to review this and comment on any possible mistakes in this calculations.

Thanking you Very much

Aluminum is 400 Microns wide, how thick it has to be to support 3.5 Amps?

Width of Aluminum is 400
Required Current I = 3.5 Amps

Operating voltage 3.3 V D.C

I assume J ( Current Density ) to be 10 e 5 A/cm2 = 1 milli Amps per Micro Meter Square

I = 3.5 A
J = I / A
A = I / J
3.5 / 1 10 -3
A =3500 Micrometer Square
A = W * T
W = 400 Microns
So T = 3500/400 = 8.75 Micrometer ( Micron )

Gangadharan Sivaraman
- Lubbock, Texas

A. Hi, Gangadharan. Your conversion factors and math appear correct.

So, assuming the allowable current density is 100,000 A/cm2 as your calculation asserts, then 8.75 micrometer thickness would be the correct answer. However, Mandar suggested a 50 to 100 percent safety factor.

I don't think that your allowable current density can be correct. I don't have experience in this field, but it sounds a good 10X too high to me based on some quick reading.


Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

March 5, 2012

I am looking for Aluminum bus bars used to carry 63 amps of current through it.
My concern is -
1)How to arrive or calculate cross sectional area required for the same?

2) What coating/finishing should we give on to bus bars to avoid galvanic corrosion?

Abhishek Bhat
- Bangalore, Karnataka, India

March 6, 2012

Hi, Abhishek. In the plating and anodizing area, where bus bars tend to be, say, 5 to 50 foot long, and the current is low voltage DC, we figure 1000 Amps/sq. in. for copper bus bar and half of that for aluminum. So you would be looking for 0.125 square inches (1/4 x 1/2 inch or 1/8 x 1inch).

I'm not quite picturing the galvanic corrosion situation, but ideally the surface of all the metals should be the same metal, i.e., if you are connecting to copper bus you would ideally copper plate the aluminum.


Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

November 4, 2013

Q. Hi. Please tell me what is thickness of Aluminum strip for 150A required, and formula to measure current through Aluminum strip? And also tell me the formula to design transformer for 15KvA load?

Farrukh Ahmed
- Islamabad, Pakistan

December 4, 2013

Q. I have in a customer's place 3150 kVA vector group Dyn11, 22kV/ 433 V AC with OLTC and loaded to about 2750 kVA. I have used 4 runs of 150 x 12 mm Aluminum flats for phases & half of that in neutral. The non linear population is about 20%. I notice a very high temperature rise and vibration.
Can I have some guidance from specialists?

NATARAJAN kadayam ramakrishnan
Retired - Coimbatore, India

December 10, 2013

A. Hi NATARAJAN. This is a specialty site for metal finishing, and most of our readers would not be familiar with electrical engineering of AC bus bar systems. Rather, most of us are only familiar with issues concerning the finishing of bus bars, or possibly the practical application of DC bus bars in electroplating and anodizing plants. We're happy to post your inquiry and any responses, of course, but I don't have the expertise to help you personally, nor even to properly curate the responses you may receive. Sorry.


Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

May 14, 2019

A. As a general rule aluminum will handle 60% of what copper will handle. So a 1"x4"x12' aluminum bar will handle 2400 amps with no problems of heating. As compared to copper the same size which will handle 4000 amps. That has been our experience and if someone disagrees please let us know.

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Drew Nosti, CEF
Anodize USA
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